1. Field of the Invention
This invention relates to chain-type power transmission belts and, more particularly, to a chain-type power transmission belt that is particularly adaptable to vehicle transmission systems, such as those on automobiles.
2. Background Art
Flexible endless chain belts made up of pivotably joined and meshed primary and secondary link plates are known in the art. Typically, laterally extending pins connect the link plates and also serve as mounting elements for movable tip members/blocks which engage the surface defining the pulley grooves which receive the belt. These tip members/blocks are spaced at regular intervals longitudinally of the belt and are successively brought into engagement with a pulley as the belt is advanced in operation.
To effect positive drive with the above-type belts, it is important that the tip members/blocks establish a substantial contact area with the pulley. To accomplish this, the tip members/blocks are each provided with an inclined surface for engagement with the pulleys. The inclined surfaces are angularly oriented to be generally parallel to the surfaces of the walls defining the pulley groove which they engage. To maximize the contact area between the tip members/blocks and pulley, the tip members/blocks are commonly attached to the pins so as to be movable relative thereto in substantially a universal-type pivoting motion.
One example of such a structure is shown in U.S. Pat. No. 4,798,567, to Hoshiro et al. In Hoshiro et al, a ball and socket-type connection is established between opposite ends of each pin and tip members/blocks attached thereto. As the tip members/blocks initially engage the pulley, the tip members/blocks tend to be reoriented to facially engage the laterally outer tip member/block surfaces with the confronting pulley surface. The facial engagement between the tip member/block surfaces and pulley is desirable not only from the standpoint of its increasing drive force, but also in that it suppresses vibration of the belt, minimizes twisting of the belt, and avoids detrimental impacts between the tip members/blocks and pulley that generate noise and/or progressively cause damage to the tip members/blocks and/or pulley. Instead, the pulley surface contacting the tip members/blocks exerts a torque on the tip members/blocks to effect rotation/pivoting of the tip member until the tip member/block surfaces and pulley surface assume a parallel, facially engaging relationship.
Heretofore, the cooperating pin ends and tip members/blocks have had to be manufactured to very close tolerances. Generally, conventional ball and socket connections result in a tight fit between the pin ends and tip members/blocks. In the absence of a close fit between the tip members/blocks and pin ends, the tip members/blocks have a tendency to fall off in use. The result of this is that the belt will run unevenly and vibrate and excessive wear will inevitably result on the system.
A further problem with a close connection between a tip member/block and pin end is that there results a considerable resistance to repositioning of the tip member/block. As a consequence, a substantial friction force is developed between the tip members/blocks and pins and may result in wear on both the tip members/blocks and pins that may precipitate premature belt failure.
Also, when the tip member/block closely embraces the pin end, there is a tendency for noise to be generated as relative movement occurs therebetween. There is also a problem with noise generation between the belt and pulley when the tip members/blocks do not rapidly reposition to properly align with the pulley. If the tip members/blocks are tightly held on the pins, the tip members/blocks may impact the pulley in a skewed position.
A further problem with prior art belts is that each tip member/block is normally unrestrained in its range of rotation relative to its associated pin. This may result in an improper orientation of certain of the tip members/blocks which creates gaps in the belt, which may result in vibration, noise generation, uneven wear on the belt, and ultimately disengagement of the tip members/blocks from their associated pin. Freely rotatable pins may also rotate excessively, develop friction and cause wear between both the tip members/blocks and pin and tip members/blocks and pulley in use.
Another problem with prior art systems is that they generally do not adapt readily to variable speed pulley configurations. In such variable speed pulleys, cooperating pulley parts are movable axially towards and away from each other to vary the effective width of the pulley groove and therefore the effective/pitch diameter of the pulley. As the pulley groove width is varied, the point of contact between the tip members/blocks varies in a radial direction which, with conventional systems, would cause misalignment of the tip member/block surfaces and pulley surface. This results in most conventional systems in a reduced contact area between the tip members/blocks and pulleys, which could cause ineffective drive transmission, and excessive and uneven wear between the tip member/block surfaces and pulleys.
Certain prior art systems have tip members/blocks that rotate with the mounting pin therefor. In these systems, if the belt and/or pulley are misaligned, the belt may twist so as to cause a torsional stress between the pin ends. Pin fracture frequently results.